An area of particular commercial interest is ceramic articles and ceramic coatings. Ceramic coatings are commonly used in products that store, treat, or transport water and liquid waste. Ceramic toilets, urinals, bidets, bathroom basins (collectively known as sanitary ware), flooring tiles and other bathroom fixtures are probably the most common example of such products.
Ceramic glaze layers further are commonly affixed to tiles and other articles used for wall tiling. In this product application, the tiles typically are larger and the glaze layer significantly thinner than floor tiles.
Ceramic products often become stained by scum and films of biologic origin (e.g., bacteria, fungus, mold, mildew). To date, the primary method of removing biological scum and film from these ceramic products has been to abrade the ceramic surface in the presence of a topical cleaning agent.
Generally, ceramic glaze compositions are unpredictably sensitive to the introduction of metallic additives, the latter frequently causing negative structural and/or aesthetic consequences in a fired glaze. In view of this fact, a person having ordinary skill in the ceramic art reasonably would expect the introduction of additional metallic compounds into a ceramic glaze base to negatively affect any one or more of the pre-fired physical properties of the ceramic glazing composition; the parameters of the firing process; and most critically, the structure of the fired glaze layer and/or the desired biocidal effect.
Wall tile applications typically employ a thin glaze layer as compared to ceramic glazed tiles intended for use in flooring or countertops: on the order of about 5-15 um as compared to about 100 um for floor tile. Thin-layer ceramic glazing compositions in particular are exquisitely susceptible to the above technical challenges.
There is a need for a thin-layer ceramic glazing composition that can impart built-in protection against the growth and proliferation of microbes to a fired glaze layer formed therefrom. However, existing technologies are somewhat limited in this regard. For example, the high temperatures used in ceramic firing processes typically preclude the use of organic biocidal agents.
At efficacious levels, conventional inorganic silver-based antibacterial compounds (e.g., zeolite, amorphous glass, sol-gel) generally are too expensive for commercial use. Moreover, incorporation of silver-based biocidal agents into ceramic glazes routinely presents issues of clouding, crazing, discoloration, and other undesirable consequences to the glaze aesthetics.
Zinc oxide is known as having biocidal characteristics and has been used in the preparation of ceramic glazing compositions. However, known ceramic glazing compositions that rely solely upon zinc oxide as a biocidal agent have not shown biocidal efficacy sufficient for control of microbial growth and proliferation on ceramic surfaces. High levels of zinc-based additives—that is, at levels high enough to confer a durable biocidal property to the glaze layer—further cause clouding, opacity, marbling, or other negative optical effects in the glaze layer, rendering them unsuitable for use in commercial products. Zinc also is incompatible with some segments of the glaze color palette.
Accordingly, there is a need for a thin-layer ceramic coating that offers persistent built-in biocidal protection while being aesthetically and optically neutral.